Indeed, such DNA swapping was the driving force in the evolution of unicellular organisms, Woese argues. Biologists have traditionally credited this so-called horizontal gene transfer with just a minor role in cellular evolution. But Woese asserts that only by sharing their genesor evolutionary inventions, as he calls themcould simple cellular organizations have given rise to more complex cell designs. In the beginning, he says, primitive cells "did not have stable genealogical records." But eventually, these linesincluding the three that spawned all extant life formsreached what Woese terms the "Darwinian threshold," the point at which a lineage matures to genetic stability. Here the cellular organization became fixed, leading to a traceable cell line via reproduction. "Crossing a Darwinian threshold leads to a more solidified, organized cellular design," he explains.
The idea could overturn conventional cell evolution wisdom. Instead of the individual, "it is the community as a whole, the ecosystem which evolves," Woese remarks. "We can¿t expect to explain cellular evolution if we stay locked in the classical Darwinian mode of thinking," he adds. "The time has come for biology to go beyond the Doctrine of Common Descent."